Sometimes Microsoft Windows will do something crazy and you can no longer get the Start > Shutdown process to work. Most will push and hold the power button until the system halts, then restart. There may be two other things you can do:
Use the shutdown.exe command: This utility will send a remote (or local) shutdown command to a system. Entering shutdown /r /m \\servername /f /t 10 will send a remote reboot to a system. Shutdown.exe is current on all modern Windows systems; in older versions, it was located on the Resource Kit. For more details, read this Microsoft KB article on the shutdown.exe command.
Use PowerShell Restart-Computer: The equivalent of the command above in PowerShell is: Start-Sleep 10 Restart-Computer -Force -ComputerName SERVERNAME